High yield, eco-friendly recycling method of polylactic acid using supercritical or dense gas carbon dioxide

Abstract

A recycling method of polylactic acid in a single step by using supercritical or dense gas carbon dioxide is provided. The recycling method includes the steps of adjusting a temperature of a reactor to at least 120° C., and adjusting a pressure to values above or below a critical pressure of carbon dioxide, wherein the critical pressure is 73.8 bar.

What is claimed is: 
     
       1. A method for a conversion of polylactic acid into lactide in a single step, wherein a reaction is performed in a carbon dioxide medium. 
     
     
       2. The method according to  claim 1 , wherein the carbon dioxide medium is a supercritical carbon dioxide medium. 
     
     
       3. The method according to  claim 1 , wherein the carbon dioxide medium is a dense gas carbon dioxide medium. 
     
     
       4. The method according to  claim 2 , comprising the following steps of:
 a) adjusting a temperature of a reactor to at least 120° C., 
 b) adjusting a reactor pressure to values above a critical pressure of carbon dioxide, wherein the critical pressure is 73.8 bar, 
 wherein the steps of a) and b) are applied at a desired sequence. 
 
     
     
       5. The method according to  claim 3 , comprising the following steps of:
 a) adjusting a temperature of a reactor to at least 120° C., 
 b) adjusting a reactor pressure to values less than a critical pressure of carbon dioxide, wherein the reactor pressure is in a range of 10 bar to 73 bar, 
 wherein the steps of a) and b) are applied at a desired sequence. 
 
     
     
       6. The method according to  claim 1 , comprising the following steps of:
 a) carrying out a heating and a pressurization gradually, 
 b) filling a reactor with carbon dioxide at a temperature and a pressure ensuring a loaded carbon dioxide remains in a gas phase, 
 c) increasing a temperature of the reactor to a reaction temperature, 
 d) filling the reactor with the carbon dioxide to a reaction pressure. 
 
     
     
       7. The method according to  claim 1 , wherein a reaction time is at least 10 minutes. 
     
     
       8. The method according to  claim 2 , wherein a reactor pressure is in a range of 74-300 bar, and a maximum pressure does not exceed a pressure endured by a reactor. 
     
     
       9. The method according to  claim 3 , wherein a reactor pressure is in a range of 10-73 bar, and a maximum pressure does not exceed a critical pressure of carbon dioxide and does not exceed a pressure endured by a reactor. 
     
     
       10. The method according to  claim 2 , wherein a reactor temperature is in a range of 120-390° C., and a maximum temperature does not exceed a temperature endured by a reactor. 
     
     
       11. The method according to  claim 3 , wherein a reactor temperature is in a range of 120-390° C., and a maximum temperature does not exceed a temperature endured by a reactor. 
     
     
       12. The method according to  claim 2 , comprising the following steps of:
 a) carrying out a heating and a pressurization gradually, 
 b) filling a reactor with carbon dioxide at a temperature and a pressure ensuring a loaded carbon dioxide remains in a gas phase, 
 c) increasing a temperature of the reactor to a reaction temperature, 
 d) filling the reactor with the carbon dioxide to a reaction pressure. 
 
     
     
       13. The method according to  claim 3 , comprising the following steps of:
 a) carrying out a heating and a pressurization gradually, 
 b) filling a reactor with carbon dioxide at a temperature and a pressure ensuring a loaded carbon dioxide remains in a gas phase, 
 c) increasing a temperature of the reactor to a reaction temperature, 
 d) filling the reactor with the carbon dioxide to a reaction pressure.